Woven wire mesh has been manufactured for many years and has a multitude of uses including, but not limited to conveying and filtration. Meshes vary in their composition and this dictates how dense or coarse the openings are within the mesh. The particular application of the woven wire mesh also dictates what size mesh is used, be it for product retention, air flow requirements, relative belt strength, etc. Certain applications require a low open area percentage belt and a dense mesh. Using a tight weave with smaller gage wire will generally result in a belt that has very small openings and a low percentage open area. However, in some cases, in order to achieve an even tighter open area requirement or more uniform belt surface, multiple strands of spirals are nested together along with multiple connecting rods creating a belt type referred to as compound-balanced belting. There can be two, three, four, or five spirals and connecting rods nested together in this type of belting. One of the inherent problems with tightly woven belts, such as compound-balanced belting, is its need for auxiliary tracking mechanisms such as rollers or edge guides. Another limiting aspect of such a tightly woven wire conveyor belt is that because of its mass, the belt requires a tremendous amount of friction to drive it. This comes from a tensioning system that is sometimes hydraulic in construction, as well as a relatively large drum (typically 24″-36″ in diameter), thus requiring a large amount of space for such an installation.
Prior art shows that there are multiple inventions that positively drive woven wire belts by use of a sprocket “tooth” that engages inside the spiral opening itself as there is an opening to do so. A known woven wire mesh includes a plurality of helically-wound spiral wires disposed between two connector rods which are positioned to be sequentially adjacent in the lengthwise direction of belt assembly and intended travel. Such combination of a helically-wound spiral and associated connector rods defines a plurality of widthwise side-by-side open-access recesses. Such recesses extend across the width of the belt and are utilized in shaping roll protrusions for uniform belt drive and increased drive contact across the width of the belt. That is, parallelogram-shaped protrusions or teeth are machined on the surface of a drive roll or sprocket so as to interfit with the confronting surface openings of the conveyor belt. Thus, a drive roll or sprocket having specially-shaped protrusions provides for uniform drive across the belt width and increased widthwise dimensional drive contact. A woven wire conveyor system of this type is disclosed in U.S. Pat. No. 6,041,916, the entire contents of which are hereby incorporated by reference.
However, where the mesh is very dense, such as in a tightly woven balanced belt or compound balanced construction, the above method of driving the belt utilizing sprocket protrusions is not a viable option as there is no room for a tooth to fit into the spiral opening.
Another limiting factor in positive-drive belting systems that use teeth engaged in openings is the engagement problem that can occur due to the belt's thermal expansion in width. When thermal expansion occurs to the belt along its width, the driving sprocket or toothed roll does not expand with it or at the same rate. The engagement issue crops up when the teeth on the sprocket or roll do not match the openings of the belt along its width. As the mesh becomes denser and wider, the belt can expand more than the machined teeth can handle, thus creating a thermal expansion problem.
Hence, while compound-balanced belting may exhibit outstanding performance and has enjoyed substantial commercial success, the necessity for auxiliary tracking mechanisms and the large friction drive requirements impose a potential limitation on utilizing such belting to its fullest capability. Accordingly, there exists a need in the marketplace for a compound-balanced woven wire conveyor system that can overcome these inherent issues conventionally experienced with compound-balanced belting.